Various in-vehicle radar apparatuses using millimeter waves have been designed. Some radar apparatuses are angle-scanning radar apparatuses that transmit a transmission beam while performing antenna scanning within a predetermined scanning-angle range and that detect a target in accordance with a reception signal reflected by the target.
In such an angle-scanning radar apparatus, however, the transmission range of a transmission beam has a fan shape. Thus, as the distance from a vehicle in which the angle-scanning radar apparatus is provided increases, a detection range increases. In contrast, as the distance from the vehicle decreases, the detection range decreases.
In order to solve the above-mentioned problem, an angle-scanning radar apparatus is disclosed in Patent Document 1. The angle-scanning radar apparatus includes a plurality of antennas having slightly different directivity directions so that setting for long distance or short distance can be performed by changing the combination of antennas to be used for transmission and reception. More specifically, the radar apparatus improves the azimuth resolution for long distance by reducing the transmission-beam width using a plurality of antennas that are adjacent to each other and increases the detection range for short distance by increasing the transmission-beam width using antennas whose number is less than the number of antennas to be used for the long-distance detection.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 8-334557
However, known general angle-scanning radar apparatuses are not capable of detecting a target located outside a scanning-angle range. For example, it is difficult to discriminate whether the peak of a reception signal detected at the outermost angle (an edge of the scanning-angle range) corresponds to a target located in the direction of that angle or corresponds to a target located outside the range.
In addition, the radar apparatus described in Patent Document 1 requires the use of a plurality of antennas. In the case of controlling transmission beams using the plurality of antennas, the radar apparatus requires a control switch group and requires the execution of complicated control processing for controlling the switch group. Furthermore, since different antennas are to be used for long-distance detection and short-distance detection, different types of operation control are necessary for the long-distance detection and the short-distance detection.